white spot on crabs leg

[mallooorryy]

Hi all, one of my smaller PPs has a fairly big white spot on his leg and i’d really appreciate any guesses as to what it is or advice for help if it’s something bad. He should be due to molt soon, but i haven’t seen this kind of thing before. idk how to put pictures on here so ill describe it. it’s a decent size, not just a tiny dot but enough to really notice. it’s not on the segment of his leg with the toes but the meatier segment above it. it’s on his farthest leg, so i think it might have just hit something? do they get bruises like that? ik he likes to climb and fall a lot. thanks for any help.